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Imagery @ 5PM: Cut-Off Low and Rio Rips!

 
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windfind



Joined: 18 Mar 1997
Posts: 698

PostPosted: Wed Aug 15, 2012 7:50 pm    Post subject: Imagery @ 5PM: Cut-Off Low and Rio Rips! Reply with quote

Hi Gang,

Below is a graphic I made of the Cut-Off Low WSW of the Bay Area at 5PM today. You may recall that I issued a Marine surge ALERT last Thursday for this Cut-Off Low to create a marine surge yesterday. This is one of those times when the marine surge alert came true and Sherman Island ripped yesterday and today.

Looking at the bottom image notice the counter-clockwise spinning flow of the Cut-Off Low. The actual low is at about 18K feet at the 500mb level but it is stirring the surface clouds you see in the image. Looking at the thicker green arrows notice that this has created southerly flow along the coast.

Now look at the thinner green arrows and notice how the the coast range creates a barrier to this cool heavy air despite the strong pressure gradient to the Central Valley. So the marine layer clouds do not penetrate inland much until it finds near sea level gaps in the coast range such as the Hwy. 92 gap, the Golden Gate gap and the Alamany gap that feeds the Stick in southerly flow. So today you will find high wind at sites downwind of those gaps.

Notice all the thunderstorms in the Sierra. What is causing them?

Tomorrow the Cut-Off Low is modeled to move west of the Oregon coast. The North Pacific High has been pushed into the Gulf of Alaska.....

So why will the Bay Area have weaker winds tomorrow?

So why will the Gorge have another day of zero to weak EAST winds tomorrow?

And you always hear me saying that Cut-Off Lows meander almost unpredictably since they disconnected from the steering upper level winds that are critical in model forecasting. But, if the models are to be believed, it looks like the Cut-Off Low will almost die then reform and return west of the Bay Area next Tuesday. So for fun I will issue a cocky MARINE SURGE ALERT for early next week.

Have fun!

Mike Godsey
weatherflow.com
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goinoff



Joined: 01 Feb 1998
Posts: 153

PostPosted: Thu Aug 16, 2012 12:02 pm    Post subject: Reply with quote

Thanks for the weather analysis. Cool Stuff..

I've always found that southerly winds w/fog for coastal buoys w/onshore pressure gradient > .08 = Excellent San Luis Res and Sherman Island fun.

It would be cool if your maps had pressure gradients displayed with current
bay/coast to central valley pressure differences.
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gregorvass



Joined: 21 Nov 1996
Posts: 1108
Location: Behind You

PostPosted: Thu Aug 16, 2012 12:51 pm    Post subject: Reply with quote

http://www.prh.noaa.gov/hnl/graphics/npacloop.gif
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